8.2.3. How to use Unit Tests

Verify that the unit testing framework is working as expected:

.\fox.ps1 waf build_app_host_unit_test
.\fox.ps1 waf build_app_host_unit_test --coverage

Typical usage and more information on the unit tests can be found in Unit tests.

8.2.3.1. Default Includes

The default include paths are defined in app_project_win32.yml and app_project_posix.yml in the key :paths: → :include:.

When a tests requires specific include-paths to be added the macro TEST_INCLUDE_PATH("../../path/to/directory") can be used. The include needs to start with ../../ and then specifies the path to the directory as seen from the repository root, e.g., to include the directory src/app/driver/config use TEST_INCLUDE_PATH("../../src/app/driver/config"). The path must be provided in POSIX form (i.e., forward slashes).

8.2.3.2. Additional Source files

If a test requires additional files to be compiled that cannot be derived from the list of included files, then the macro TEST_SOURCE_FILE("file-name.c") can be used.

8.2.3.3. Guidelines for the Unit Test Skeleton

Note

This example

In this example a driver that resides in src/app/driver/abc/abc.c and src/app/driver/abc/abc.h is added and therefore the accompanying unit tests need to be added also. The module abc.c implements the public function extern uint8_t ABC_DoThis(void) and the static function static uint8_t ABC_DoSomethingElse(uint8_t someArgument). Therefore, there are now two functions that need to be united tested.

At first the accompanying unit test file needs to be created in tests/unit/app/driver/abc/test_abc.c (notice the prefix test) based on the template in conf/tpl/test_c.c. The helper script tools/utils/generate_missing_test_files.py can be used to automatically create the file.

8.2.3.4. Public/Extern Function Tests

  1. Add a function uint8_t testABC_DoThis() in the appropriate section in the test file tests/unit/app/driver/abc/test_abc.c. This function implements the tests for ABC_DoThis(). The prefix test (no trailing underscore) is required for ceedling to detect the function as a test-function.

  2. Write the test code.

8.2.3.5. Static Function Tests

  1. Static functions are not seen by other translation units, therefore the static functions must be made callable from other modules by creating a wrapper. For this example the wrapper will be extern uint8_t TEST_ABC_DoSomethingElse(uint8_t someArgument) (notice the TEST_ prefix followed by the name of the static function).

  2. The declaration of the wrapper needs to be placed in the appropriate section in the header of the driver (src/app/driver/abc/abc.h).

  3. The definition of the wrapper needs to be placed in the appropriate section in the source of the driver (src/app/driver/abc/abc.c). The only thing this wrapper needs to do, is to verbatim pass all arguments to the original function (i.e., the static function) and return its result. The definition of the wrapper looks therefore like this

    1extern uint8_t testABC_DoSomethingElse(uint8_t someArgument) {
2    return ABC_DoSomethingElse(someArgument);
3}

  4. Add a function void testABC_DoSomethingElse(void) in the appropriate section in the test file tests/unit/app/driver/abc/test_abc.c. This function implements the tests for ABC_DoSomethingElse(). The prefix test (no trailing underscore) is required for ceedling to detect the function as a test-function. Note: The TEST_ prefix of the externalization wrapper is removed and not part of the test function name.

  5. Write test code.

8.2.3.6. Result

Listing 8.47 Header of the abc-driver (src/app/driver/abc/abc.h)
1/*========== Extern Function Prototypes =====================================*/
2extern uint8_t ABC_DoThis(void);
3
4/*========== Externalized Static Functions Prototypes (Unit Test) ===========*/
5#ifdef UNITY_UNIT_TEST
6extern uint8_t TEST_ABC_DoSomethingElse(uint8_t someArgument);
7#endif

The wrapper function TEST_ABC_DoSomethingElse needs to be put inside the UNITY_UNIT_TEST guard, so that it is not build during target builds.

Listing 8.48 Implementation of the abc-driver (src/app/driver/abc/abc.c)
 1/*========== Static Function Prototypes =====================================*/
 2static uint8_t ABC_DoSomethingElse(uint8_t someArgument);
 3
 4/*========== Static Function Implementations ================================*/
 5static uint8_t ABC_DoSomethingElse(uint8_t someArgument) {
 6    return someArgument;
 7}
 8
 9/*========== Extern Function Implementations ================================*/
10extern uint8_t ABC_DoThis(void) {
11    return 1u;
12}
13
14/*========== Externalized Static Function Implementations (Unit Test) =======*/
15#ifdef UNITY_UNIT_TEST
16extern uint8_t TEST_ABC_DoSomethingElse(uint8_t someArgument) {
17    return ABC_DoSomethingElse(someArgument);
18}
19#endif
Listing 8.49 Implementation of the abc-driver test (tests/unit/app/driver/abc/test_abc.c)
1void testABC_DoThis(void) {
2    /* test code */
3    ABC_DoThis();
4};
5
6void testABC_DoSomethingElse() {
7    /* test code */
8    TEST_ABC_DoSomethingElse(2);
9}

8.2.4. How to exclude files from unit tests

Normally, all files should be covered by a (at least empty) unit test. If a certain file is not meant to be covered by unit tests, it has to be excluded in several locations in order to suppress checking mechanisms in the toolchain.

Additionally, the main wscript contains a mechanism that checks that every file has a corresponding test file in the proper location. Untested files have to be added to excl in check_test_files(ctx).

8.2.5. Using ceedling directly

Warning

Ceedling (the unit test runner that is used by this project) is wrapped by the Waf toolchain. The toolchain makes sure that the path handed to ceedling contains the necessary applications and files, so without the wrapper extensive knowledge of the project structure is helpful.

That being said, it is normally not necessary to directly execute ceedling as the wrapper handles this.

The wscript of this project executes always the complete unit test-suite. This can take some time. When developing or debugging a unit test, it might be beneficial to have finer control over which test is executed.

For this and especially for debugging the unit test integration it is possible to directly access ceedling as follows:

.\fox.ps1 ceedling gcov:test_plausibility.c

8.2.6. Linux specific Usage

The unit test suite is developed on Windows and there works out of the box on all setup that install the dependencies as they are specified in Software Installation. However, it is still possible to get the unit test suite working on Linux. Internally it is tested with the following setup:

  • cat /etc/redhat-release: Red Hat Enterprise Linux release 8.8 (Ootpa)

  • uname -mrs: Linux 4.18.0-425.19.2.el8_7.x86_64 x86_64

  • gcc --version: gcc (GCC) 8.5.0 20210514 (Red Hat 8.5.0-18)

  • ruby --version: ruby 3.1.2p20 (2022-04-12 revision 4491bb740a) [x86_64-linux]